Thermal expansion and bandgap properties of bi-material triangle re-entrant honeycomb with adjustable Poisson's ratio

The future mechanical metamaterials should achieve multifunctional integration to meet the requirements of structures and materials in the aviation field for service in complex environments. In this paper, a bi-material triangle re-entrant honeycomb (BTRH) with the tunable coefficient of thermal expansion (CTE), Poisson's ratio (PR), and bandgap is proposed. Analytical analysis and numerical simulations are implemented to quantify the evolution of the effective CTE, PR, and Young's modulus. Experiments are conducted to verify the correctness of the theory of the effective PR and Young's modulus. Based on Bloch's theorem, the band structures of the BTRH are calculated by finite element analysis, and the correctness of the band structure calculation is verified by calculating the transmission characteristic curve. The effects of geometric parameters and material combinations on the mechanical properties are investigated systematically. The results of analytical and numerical simulations exhibit that the CTE and PR can be coupled with regulation from positive to negative through changing the geometry configuration and material combinations of the BTRH. Meanwhile, the function of tunable bandgap and large total effective bandgap width can be obtained. This work provides an important reference for the rational design of multifunctional metamaterials to maintain shape stability and efficient sound insulation.